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Wednesday, July 24, 2013

EIA: Underground Natural Gas Working Storage Capacity

Natural gas working storage capacity increased by about 2 percent in the Lower 48 states between November 2011 and November 2012. The U.S. Energy Information Administration (EIA) has two measures of working gas storage capacity, and both increased by similar amounts:

Maximum demonstrated working gas volume is an operational measure of the highest level of working gas reported at each storage facility at any time over the previous five years, according to EIA's monthly survey of storage operators. Working gas is the volume of natural gas in an underground natural gas facility available to be withdrawn, not including base gas.

The maximum demonstrated working gas volume is a practical measure of full storage. Filling storage, which requires compressors to inject the gas into the storage facility, becomes more difficult and expensive as storage volume nears its maximum and pressures inside the facility increase.

That's why the demonstrated maximum is generally less than the design capacity, averaging 93% over the past two measurement periods (see Table 1), and why any given week's storage inventory is generally less than the demonstrated maximum. The maximum demonstrated volume provides guidance to operators and market analysts on the economics of filling the system.

Last October, for example, when working gas in storage reached a record-high of 3,930 Bcf, a simple calculation using the then current maximum demonstrated volume (4,188 Bcf) showed storage to be 94% full.